SGER: Soil-Structure Interaction of Bridge Columns in Frozen Environments, CMS-0502117
PI: Sritharan, Iowa State University
The seasonal freezing that occurs in much of the U.S. is expected to significantly influence the lateral behavior of civil structures, especially bridges. Research on material behavior shows that at temperatures near -20 degrees C concrete properties are altered by 20 to 50 percent, ductility of steel may be completely lost, and soil properties are enhanced by up to two orders of magnitudes. Consequently, the lateral load response of structures, which is dictated by soil-foundation-structure interaction and the ductility capacity of structural members, is dependent on environmental conditions. With the potential for large seismic events in various states that experience seasonal freezing, an investigation of the temperature effects on the lateral load response of soil-foundation-structure systems becomes of paramount importance.
This project explores temperature effects on soil-foundation-structure systems by studying bridge Columns supported on cast-in-drilled-hole (CIDH) pile shafts. Through a large-scale outdoor Experimentation, lateral load responses of three bridge columns in warm and frozen ground conditions will be studied to understand the seasonal temperature effects on soil-structure interaction as well as system ductility. A preliminary analytical investigation revealed that freezing conditions at a ground temperature near -20 degrees C may reduce structure displacement capacity by 70% and increase column shear demand by 35%, due to relocation and reduction in spread of plasticity in the pile shaft. An analytical study utilizing the measured material properties and in-situ soil test data will be performed to characterize the responses of the three bridge column systems. Comparing the analytical and experimental results, seismic design implications of the effects of seasonal freezing on soil-foundation-structure systems will be presented. In addition, a plan for detailed investigation on this subject area will be developed.
The results of the proposed exploratory study are expected to improve design of soil-foundation-structure systems under extreme lateral loads such as those induced by earthquakes, thus contributing to construction of safer, more reliable structures in regions that experience seasonal freezing.